In AWD systems using a hydraulic power source there is in some applications a demand of an added locking function during key off. For example, the vehicle may be parked on a hill and during this condition torque distribution to all wheels is desired. As it is not possible to guarantee a complete leakage free solution over life time, it may be preferred to lock the AWD coupling mechanically instead of using a compressed volume of oil behind a piston that compresses a disc package of the AWD coupling. Furthermore, a mechanical lock system could also be used for unloading the hydraulic power source of the AWD coupling in some off road driving situation, such as sand driving.